Since Jul. 1, 1980, the date of the first testing of the electronic directory service at Saint Malo, the Minitel has been using, in France, a transmission speed of 1200 bps to receive reference service information and a speed of 75 bps to transmit keyboarding of the user. This mode of transmission, in full duplex, is based on V23 modulation which is a speed of 1200/75 bps between the Minitel and Videotext Access Point (PAVI) units. The connection between Minitel and PAVI is based on the switched telephone network (RTC). The connection between PAVI and the Teletel servers is based on the TRANSPAC network with transmission speeds of 19.2 kbps or 48 kbps.
At the beginning of the 1990s, in order to improve convenience and speed in consulting Teletel services, provision was made to increase the transmission speed at first to 4800 bps, and then to 9600 bps between the Access Point and Minitel. This new mode of transmission in semi-duplex or half-duplex is based on the V27ter modulation for the speed of 4800 bps and on the aforementioned V29 modulation at 9600 bps. The V27ter and V29 standards have been kept for reasons of cost and performance. The speed of 4800 bps and 9600 bps can be used over the two paths, the data circuit termination unit (ETCD) or modem operating at half speed.
This new Teletel access service, called "Teletel high speed" access service (or TVR) thereby allows a useful rate of flow of communication multiplied by four in V27ter and by eight in V29 with respect to a useful throughput rate of V23 access. It thus permits a rapid transfer of pages requiring a considerable volume of information; this is the privileged channel for operation of the future photographic Minitel and for applications such as transfers of files, telecopy, audio videotext, etc.
The main public terminal (or Minitel) is not currently connectable, equally and without specific intervention of the user, over the Teletel V23 access, over V27ter Teletel access and over the forthcoming V27ter/V29 accesses with connection time similar to the present V23.
Establishment of telephone connection between the Minitel and videotext access points (PAVI) is effected principally over the switched telephone network (RTC).
Request for establishing connection consists of the actions of picking up the telephone line (or going on line) and dialing the number. This request can be at the initiative:
of the user (manual demand) PA1 of the Minitel through the intermediary of the telephone directory PA1 of a peripheral component of the Minitel such as the memory card reader or LECAM. PA1 of the user by touching a button such as the "end connection" button of the Minitel, PA1 of the Minitel through the intermediary of the telephone and videotext directory, PA1 of a peripheral device of the Minitel through the intermediary of a command sequence. PA1 physical connection in common transmission mode for the two units according to the quickest preferable modulation such as that presented in the summary table of physical connection types (case of initial communication), PA1 and/or physical reestablishment of communication in at least one mode, for example at least one of the three modes V23, V27ter and V29 (case of radio telegraphy-data or audio videotext application). PA1 a) emission by one of the units called "first matching unit" of a first matching signal stream according to a given transmission mode in half-duplex. PA1 b) analysis by the other unit, called the "second unit for matching" of the unmodulated carrier signal frequency of said first matching signal stream. PA1 c) in case of recognition by the second unit of the carrier signal frequency of said given transmission mode, placement of the second unit to receive, in accordance with said given transmission mode, of said conditioning segment. PA1 d) validation by the second unit of reception of said conditioning segment of the first matching signal stream, and conditioning of the second unit in accordance with said given transmission mode, which allows it to transmit in this mode. PA1 e) transmission by the second unit of a second matching signal stream in the recognized transmission mode which corresponds to the given mode, which validates communication for the second unit in the given transmission mode. PA1 f) analysis by the first unit of the signal frequency of the unmodulated carrier of the second matching signal stream. PA1 g) in case of recognition by the first unit of the carrier signal frequency of the given transmission mode, keeping the first unit in receiving condition in said given transmission mode recognized and accepted by the second unit. PA1 h) validation by the first unit of reception of said conditioning segment of the second matching signal stream, and conditioning of the first unit in said given transmission mode. PA1 i) establishment by the first unit of communication in said given transmission mode. PA1 stages a) and b), in which the given transmission mode is the first transmission mode. PA1 j) in case of non-recognition by unit A of the unmodulated carrier signal frequency in the first transmission mode and the impossibility of unit B of being placed in said first transmission mode, non-validation by unit B of reception of the first matching signal stream. PA1 k) stages a) to i) in which the given transmission mode is the second transmission mode, during which the first unit is unit B and the second unit is unit A. PA1 0-0) request for establishing connection by unit A (connection order). PA1 1-0) detection by unit B of request to establish connection and establishment of the connection. PA1 2-0) emission by unit B of a first signal with duration at least equal to a first given duration, of a frequency equal to that of the answering dial tone of the automatic response data unit, having a frequency that is different from the half-duplex modulation carrier stream frequency, followed by a silence having a second duration. PA1 3-0) sensing by unit A of the presence of said frequency signal during at least the first given duration. PA1 4-0) measurement by unit A of the second duration of said silence. PA1 5-0) if the second duration is greater than a given threshold duration, validation of execution of stages a) to i) or of stages a) to k), for which the first unit is unit A and the second unit is unit B. PA1 analysis by unit A of the carrier frequency of a said matching signal stream, PA1 in case of recognition of said frequency in the first transmission mode, validation of stages a) to i) according to the second transmission mode, during which the first unit is unit B and the first sic! unit is unit A. PA1 12-1) sending by unit A of a first matching signal stream in a first transmission mode. PA1 12-2) search by unit B for the presence of the carrier signal frequency. PA1 12-3) in case of non-recognition by unit B of the carrier signal frequency corresponding to the second transmission mode, following a waiting time greater than a given duration threshold, validation of execution of stages a) to i) according to the second transmission mode, during which the first unit is unit B and the second unit is unit A. PA1 13-1) release of half-duplex communication successively at logical levels of the communication protocol then at the physical level (for example, because of loss of carrier) while maintaining connection between the units. PA1 13-2) passage in radio telegraphy mode during a certain delay time duration. PA1 13-3) sensing of the end of the time delay duration. PA1 13-4) validation of execution of stages a) to i) or of stages a) to k). PA1 14-1) before the end of the relative time delay duration in radio telegraphy mode, initialization by one of the units of communication, by emission of an order for communication, for example a segment of given duration of the unmodulated carrier frequency, which occurs during the telephony mode. PA1 14-2) validation of the execution of stages a) to i) of claim 1 or of stages a) to k). PA1 15-1) program the emission by the modem of a stream of matching signals preceded by an unmodulated carrier signal, PA1 15-2) program sensing by the modem of at least one unmodulated carrier frequency located at the beginning of a received matching stream, and to place the modem in half-duplex transmission mode corresponding to said carrier frequency in order to allow the modem to receive the other signals of said received matching stream, and PA1 15-3) program a validation of physical communication in half-duplex according to said transmission mode once the modem has received and transmitted in the proper manner a said matching signal stream, which allows one subsequently to effect an exchange of synchronization signal streams to validate a connection in said transmission mode. PA1 reception conforming to a matching signal stream in accordance with 15-2, PA1 sensing by the modem following a request for communication of a characteristic silence interval of said unit. PA1 adjustment of the type of modulation, especially in fixing (or freezing) receiving filter coefficients PA1 resumption of transmission PA1 possibly, doubling of speed (such as V29 versus V27ter). PA1 a) initialization by the first unit of resumption-adjustment, preferably following sensing by the first unit of at least one erroneous synchronization signal stream, and preferably two successive erroneous streams. PA1 b) emission by the first set of a matching signal stream in the transmission mode used previously in half-duplex for exchanges of synchronizing signal streams. PA1 c) analysis by the second unit of the unmodulated carrier signal frequency of said matching signal stream. PA1 d) in case of recognition of this frequency which characterizes a request for resumption adjustment, placing the second unit in receiving mode by a matching signal stream. PA1 e) in case of validation by the second unit of reception of the second matching signal stream, adaptation of the second unit in said transmission mode which is used, preferably by freezing the reception filter coefficients as adapted to the new transmission support characteristics. PA1 f) emission by the second unit of a stream of matching signals in the recognized transmission mode. PA1 g) analysis by the first set of the unmodulated carrier signal stream frequency of said matching signal stream. PA1 h) in case of recognition of this frequency, maintaining the position of the first unit to receive in said transmission mode. PA1 i) in case of validation by the first unit of reception of the matching signal stream emitted by the second unit, adjustment of the first unit in said transmission mode, preferably by freezing the receiving filter coefficients of the first unit. PA1 j) renewal of synchronizing signal stream exchanges, possibly followed by application information without interrupting the higher logical levels of the communication protocol of the two units. PA1 k) in case of non-recognition by the first unit of the matching signal stream emitted by the second unit, and possibly at the end of a given time delay duration, emission by the first unit of a stream of matching signals in the second mode of transmission. PA1 l) analysis by the second unit of the unmodulated carrier signal frequency of said matching signal stream emitted by the first unit. PA1 m) in case of recognition of said frequency at the time of stage 1), which therefore characterizes a request for resumption-adjustment in the second transmission mode, positioning the second unit to receive a stream of matching signals in the second transmission mode. PA1 n) in case of validation by the second unit of reception of said matching signal stream, adjustment of the second unit to the second transmission mode, preferably by freezing the receiving filter coefficients adjusted to the new transmission support characteristics and adjusted to the second transmission mode. PA1 o) emission by the second unit of a stream of matching signals in the second transmission mode in order to allow the first unit its adjustment to the second transmission mode. PA1 p) analysis by the first unit of the unmodulated carrier signal frequency of said matching signal stream emitted by the second unit. PA1 q) in case of recognition of this frequency, maintaining the position of the first unit in the second transmission mode which is being used. PA1 r) in case of validation by the first unit of reception of said matching signal stream emitted by the second unit, adjustment of the first unit to the second transmission mode, preferably by freezing the receiving filter coefficients in order to be adjusted to the new transmission support characteristics. PA1 s) renewal, in the second transmission mode, of exchanges of synchronizing signal streams, (for example, short streams in V27ter mode), possibly followed by application information without interruption of the logical levels of the communication protocol of the two units. PA1 t) in case of non-recognition of the stream of matching signals by the first unit, possibly at the end of a given time delay duration, renewal by the first unit of emission of a matching signal stream in said transmission mode. PA1 u) stages c) to j). PA1 v) in case of non-recognition by the first unit, at the time of stage g of said sequence u) of the matching signal stream emitted by the second unit, and possibly at the end of a certain time delay, the last attempt made by the first unit according to t) and u) before breaking the connection between the two sets. PA1 10-1) program initialization of resumption-adjustment, preferably following the sensing of reception by the modem of an erroneous synchronizing signal stream, without modifying the values or coefficients of the receiving filter. PA1 10-2) programming emission by the modem of a matching signal stream preceded by an unmodulated carrier signal, preferably in the same modulation as said erroneous synchronization signal stream, said matching signal stream constituting a request for resumption-adjustment. PA1 10-3) programming sensing by the modem of at least one unmodulated carrier frequency located at the beginning of a received matching stream, and placing the modem in half-duplex transmission mode corresponding to said carrier frequency in order to allow the modem to sense a request for resumption-adjustment to receive the other signals of said received matching stream and to set the receiving filter coefficients after reception of the matching stream. PA1 10-4) validate the physical adjustment resumption in half-duplex in said transmission mode once the modem has emitted and received in a manner which is in accordance with a a said matching signal stream during communication by exchange of the matching signal stream, which then permits the unit to exchange synchronizing signal streams (short streams).
Sensing this request for establishing communication by the distant unit (calling ring over the switched telephone network (RTC) or location of an indicator on the shared line) authorizes it to effect connection.
After making the connection, communication or physical connection is effected by the exchange and recognition of signals between the modems and the two units. Validation of communication allows the two units to then transmit data and to thereby establish a logical connection such as the establishment of packet and screen levels of the communication protocol used, in V27ter and in V29 for example.
The request for communication (or "order to establish communication" or even "connection order") can be at the initiative:
To communicate in V23, V27ter or V29 mode (V23/V27ter/V29) it is possible to use several "end-connection" buttons one time for each of the modes. This manual solution is not ergonomic for a large public user group.
Another solution would be to rely on preliminary and systematic communication in V23, and then, by reception of a particular sequence, to change over to V27ter or V29 transmission. This solution would be penalized in connection time, and would not allow communication with existing units exclusively in V27ter, which do not have the V23 mode.
These solutions, manual or semi-automatic, would also have the disadvantage of prohibiting or making difficult any possibility of automatic re-establishment of communication (radio telegraphy-data or audio video text application) and the disadvantage of prohibiting any process of maintaining communication (resumption of communication in V27ter or V29, and a speed doubling from V27 to V27ter).